Steam, possibly carrying radioactive elements, had been rising for two days from the reactor building, and the move lessens the chances that more radiation will seep into the air.

Added up, the power and concerted dousing bring authorities closer to ending a nuclear crisis that has complicated the government's response to the catastrophic earthquake and tsunami that devastated Japan's north-east coast 11 days ago.

Much of the broader public's concern has centred on radiation contamination of food and water. The government has already ordered a ban on spinach, canola and raw milk from the prefectures around Fukushima. The sea off the nuclear plant is showing elevated levels of radioactive iodine and caesium, prompting the government to test seafood.

However, a Japanese radiation expert, Professor Shunichi Yamashita, has claimed that life just one kilometre outside the restricted area surrounding the stricken nuclear plant leaking radiation is “as safe as London”.

Concerns about radiation in Tokyo have prompted thousands of foreigners and Japanese citizens to leave. Many businesses have relocated to the west of Japan or Hong Kong.

Officials from the International Atomic Energy Agency found radiation 1,600 times higher than normal around the town of Namie, near Fukushima. But Mr Yamashita said at a briefing at the press club in Tokyo: “People who evacuated from the 20km zone are completely safe,” he said.

It was reported yesterday that minuscule amounts of radioactive particles believed to have come from the Fukushima power plant had been detected as far away as Iceland.

The Fukushima Dai-ichi nuclear complex has leaked radiation that has found its way into vegetables, raw milk, the water supply and even seawater.

The resulting fears of contamination mean the impact has reverberated well beyond the disaster area. But for those who have been evacuated from the danger zone near the nuclear plant, anxiety is still high. Around 1,400 people are living in a gymnasium which has been turned into an evacuation centre.

As many as 2.4m people are still without water and 250,000 households have no power.

“It was an act of god,” said Yoshihiro Amano, a grocery store owner whose house is four miles from the reactors. “It won't help to get angry. But we are worried. We don't know if it will take days, months or decades to go home. Maybe never.”

Professor Yamashita, from Nagasaki University, said radiation in Tokyo was minuscule and being hyped needlessly by the media.

“We're talking about microsieverts (SI unit of radiation) a year not millisieverts,” he said. “The dose is crucial. It's nonsense to worry about microsieverts.”

Concerns about radiation in Tokyo have prompted thousands of people to leave. Many businesses have relocated to the west of Japan or Hong Kong.

The latest radiation reading over 24 hours was 0.34 microsieverts though the figure is increasing slightly. The professor said exposure to 11.4 microsieverts per hour was the safety benchmark.

Officials from the International Atomic Energy Agency found radiation 1,600 times higher than normal around the town of Namie, near Fukushima. But Mr Yamashita said at a briefing at the press club in Tokyo: “People who evacuated from the 20km zone are completely safe.”Japan's Prime Minister last week advised 140,000 people living within between 20km and 30km of the complex to leave. Many have criticised the perimeter as arbitrary. The US government says 80km is the safe limit.

Professor Yamashita said most radiation-linked illnesses in the 1986 Chernobyl disaster, including thyroid cancer, came not from direct exposure but from consuming food, especially contaminated milk. “Compared to Chernobyl the Fukushima radiation release is still very, very low,” he said. “I want the media to make this clear.”

Chernobyl, the world's worst nuclear disaster, has been linked to thousands of thyroid cancer cases since the plant in Ukraine went into meltdown.

The government has imposed a ban on food products from Fukushima and surrounding areas. Small quantities of radiation have been detected in spinach and milk. The government has also begun studying contamination of fish food after discovering radioactive materials 128 times higher than the legal limit in the seas around the plant. Japan's nuclear agency has refused to rule out the possibility that fish may be contaminated.It was reported yesterday that minuscule amounts of radioactive particles believed to have come from the Fukushima power plant had been detected as far away as Iceland.

For those people who have been evacuated from the danger zone near the nuclear plant, these are days of anxiety. Around 1,400 people are living in the town's gymnasium which has been turned into an evacuation centre and yesterday there were long queues for bowls of hot noodle soup. As many as 2.4 million people are still without water and nearly 250,000 households have no power.

“It was an act of god,” Yoshihiro Amano, a grocery store owner whose house is four miles from the reactors, told Associated Press. “It won't help to get angry. But we are worried. We don't know if it will take days, months or decades to go home. Maybe never.”

At the Fukushima complex rising temperatures around the core of one of the reactors heated a pool holding spent nuclear fuel near to boiling point raising the prospect of more radioactive steam being released.

Tokyo Electric Power Company, the plant operator, said it needed more time to stabilise the reactors. Sakae Muto, executive vice-president, said the core of the No 1 reactor was causing concern with temperatures rising to 302C. “We need to bring that down a bit,” he said.

“Injecting more water is one option [but] we need more time. It's too early to say if they are sufficiently stable.” Reuters had earlier reported that the Fukushima plant was storing more uranium that it designed to, and that in the past decade it had missed a number routine safety checks.

Government officials and health experts say the doses are low and not a threat to human health unless the tainted products are consumed in abnormally excessive quantities.

The Vienna-based International Atomic Energy Agency said that radiation seeping into the environment is a concern and needs to be monitored.

The levels drop dramatically with distance from the nuclear complex. In Tokyo, about 140 miles south of the plant, levels in recent days have been higher than normal for the city but still only a third of the global average for naturally occurring background radiation.

Case study

The earthquake and tsunami that ripped through north-eastern Japan 11 days ago has led to lots of stories of stoicism and pulling together. But not in every case. Police say that the disaster crippled a bank's security mechanisms, and left a safe wide open. That allowed someone to walk off with 40 million yen, about £300,000. The tsunami washed over the Shinkin Bank, and police said that between the wave's power and the ensuing power outages, the vault came open.